The present invention relates to semiconductor devices, and more particularly to a laminated diffusion barrier that has a low-dielectric constant, k, yet is resistant to oxygen and/or moisture permeability. Specifically, the present invention is directed to a laminated diffusion barrier that comprises alternating layers of high-permeability, i.e., high-affinity, dielectric films and low-permeability, i.e., low-affinity, dielectric films. The inventive diffusion barrier is particularly useful as a dielectric capping layer for interconnect structures that include wiring regions that are surrounded by organic interlevel dielectrics, or porous dielectrics (including organic and inorganic).
Presently in integrated circuit (IC) manufacturing, the wiring in chip level interconnects and the device itself is normally protected from oxygen and moisture by various layers of inorganic dielectrics consisting of oxides such as SiO2 or nitrides such as Si3N4. The inorganic dielectrics are typically formed on the surface of an interconnect structure which includes various wiring regions that are surrounded by various dielectric levels. For example, today""s advanced chips typically have 6-8 levels of metal wiring and thus of dielectric material.
In addition to being effective as oxygen and/or moisture barrier layers, inorganic dielectrics are also excellent barriers against the migration of ions which can be present as contaminants or in processing fluids such as chemical etchant solutions. Such ions may corrode the metal wiring as well as migrate to the semiconductor itself wherein the migrating ions may either form silicides that may essentially destroy the semiconductor device, or may cause undesirable ionic currents. Another further problem involves copper atoms or ions which are not contained in the patterned copper wiring features (i.e., line and vias), and cause undesirable electrical contact (leakage) between the patterned copper features.
Despite being successful in preventing the diffusion of oxygen and moisture, barrier layers composed of inorganic dielectrics increase the effective dielectric constant of interconnect structures. This is because many of the interconnect structures used today contain low density dielectrics (including organic and inorganic dielectrics), which have dielectric constants that are less than SiO2, as the interlevel dielectrics. The use of low-density dielectrics as the interlevel dielectrics provides faster operating devices because of the reduced signal delay.
An apparent solution to the mismatch problem caused by using an inorganic-containing diffusion barrier with an IC structure that contains a low-density dielectric as the interlevel dielectric is to switch to a laminated diffusion barrier. Low-density dielectrics tend to be permeable to moisture and other contaminants. This permeability problem is particularly detrimental to Cu wiring which can readily oxidize in the presence of moisture.
In view of the drawbacks mentioned above with prior art diffusion barriers, there is a continued need for providing a new and improved diffusion barrier that has a low-k, yet is resistant to oxygen and/or moisture.
One object of the present invention is to provide a diffusion barrier that has a low-dielectric constant, k, associated therewith. The term xe2x80x9clow-kxe2x80x9d denotes dielectric materials that have a dielectric constant of about 8 or less, preferably from about 3 to about 5.
Another object of the present invention is to provide a diffusion barrier that is resistant to oxygen and/or moisture permeability.
A further object of the present invention is to provide a diffusion barrier that is compatible with existing interconnect structures.
A yet further object of the present invention is to provide a diffusion barrier which does not sufficiently increase the effective dielectric constant of an underlying interconnect structure which contains a low-k organic dielectric as the interlevel dielectric.
These and other objects and advantages are achieved in the present invention by providing a diffusion barrier that includes very thin (on the order of 12 nm or less) alternating layers of high-permeability, i.e., high-affinity, and low-permeability, i.e., low-affinity, dielectric films. The term xe2x80x9chigh-permeabilityxe2x80x9d denotes a dielectric film in which oxygen and/or moisture can readily diffuse into, whereas the term xe2x80x9clow-permeabilityxe2x80x9d denotes a film that retards the diffusion of oxygen and/or moisture. By providing a stack of two or more of the alternating high-permeability and low-permeability films, it is possible to retard the diffusion of oxygen and/or moisture to the underlying interconnect structure.
Without wishing to be bound by any theory, it is believed that the high-permeability dielectric allows lateral diffusion of oxygen and/or moisture so that the resulting concentration of oxygen and/or moisture at the low-permeability film is lower than at the high-permeability film. With multiple alternating layers, the concentration gradient of oxygen/moisture becomes less and less. In addition to lowering the concentration gradient by dilution within the high-permeability dielectric film (i.e., the diffusion within the high-permeability film is greater than that of the low-permeability film such that lateral diffusion with the high-permeability film results in dilution of the forward concentration gradient imposed upon the low-permeability film), the chemical affinity of the high-permeability film for oxygen/moisture also removes some of the oxygen/moisture through irreversible reaction.
Specifically, the inventive diffusion barrier comprises a dielectric stack having at least two or more dielectric films, each film having a dielectric constant of about 8 or less, wherein said dielectric stack comprises alternating films composed of a high-permeability material and a low-permeability material, said high-permeability material is formed on said low-permeability material.
In one embodiment of the present invention, the diffusion barrier includes a stack of three to five dielectric films which comprises alternating layers of low-density Si, C, H or Si, C, O, H amorphous films, as the high-permeability material, formed on Si3N4 or Al2O3, as the low-permeability material. In yet another embodiment of the present invention, the diffusion barrier comprises a stack of twelve dielectric films. In this embodiment, each layer comprises a Si, C and H containing amorphous alloy, with O and N as optional elements.
Another aspect of the present invention relates to a semiconductor structure such as an interconnect structure which includes the diffusion barrier formed thereon. Specifically, the inventive semiconductor structure comprises a substrate having at least one metal region formed therein and a diffusion barrier formed on a surface of said substrate, wherein said diffusion barrier comprises a dielectric stack having at least two or more dielectric films, each film having a dielectric constant of about 8 or less, wherein said dielectric stack comprises alternating films composed of a high-permeability material and a low-permeability material, said high-permeability material is formed on said low-permeability material.
A yet further aspect of the present invention relates to a method of fabricating the inventive diffusion barrier. Specifically, the inventive method comprises forming a dielectric stack having at least two or more dielectric films on a surface of a substrate containing at least one metal wiring region, each film having a dielectric constant of about 8 or less, wherein said dielectric stack comprises alternating films composed of a high-permeability material and a low permeability material, said high-permeability material is formed on said low-permeability material.
The forming step may occur in a single deposition reaction chamber or multiple deposition reaction chambers may be employed. Moreover, the forming step may include one or more of the following deposition processes: chemical vapor deposition (CVD), low-pressure CVD, plasma-assisted CVD, atomic layer deposition (ALD), evaporation, spin coating, chemical solution deposition or sputtering.